1. Field of the Invention
The present invention generally relates to a wheel supporting structure for vehicles. More particularly, the invention relates to a wheel supporting structure for riding type working vehicles such as agricultural tractors.
2. Description of Relevant Art
In general, riding type working vehicles, such as agricultural tractors, have front and rear ground wheels, disposed at both sides of such vehicle, which are adapted in various manners for the driving and/or the steering operations of the vehicle. In most of those working vehicles, both the front and rear wheels are adapted to be driven, and in the majority of them the front wheels or sometimes the rear wheels are additionally adapted to be steered, while in the rest thereof both the front and rear wheels are steerable.
In such riding type working vehicles, for each ground wheel needed to be adapted for both driving and steering like above, there generally has been employed a supporting structure including, as in a vehicle proposed by Japanese Utility Model Publication No. 53-4583, published on Feb. 4, 1978, a reduction gearing steerably attached to a king pin and provided with an output shaft for fixing thereto the ground wheel. The reduction gearing includes an input shaft connected through a universal joint to a differential gearing disposed at the longitudinally central part of the vehicle. Such wheel supporting structure is accommodated to the well-known demand that drive wheels for riding type working vehicles should be able to stand producing large tractive forces, when necessary. Incidentally, the vehicle proposed by the Japanese Utility Model Publication No. 53-4583 was a jeep of four-wheel-drive type, in which respective drive wheels were also intended to match up to the demand for strong traction, like the above case.
Moreover, in riding type working vehicles such as agricultural tractors, it has been to enable the alteration or adjustment of vehicle level to be effected in accordance with working conditions. To answer such desideratum, conventionally there have been proposed a number of wheel supporting structures for vehicles which are to be adapted for level adjustment. As an example thereof, there was a wheel supporting structure disclosed by Japanese Utility Model Lay-Open Print No. 55-41991, laid open on Mar. 18, 1980. This supporting structure included a pair of link rods, parallel with each other and different in the length from each other, for the interconnection between a ground wheel and a vehicle body, and a hydraulic power cylinder for adjusting the working position of the parallel linkage, to thereby adjust the vertical position of the ground wheel relative to the vehicle body, permitting the vehicle level to be adjusted.
However, such conventional wheel supporting structures, which needed a power source or more particularly a hydraulic cylinder for use in level adjustment and a mechanism for controlling the hydraulic cylinder, were complicated and expensive. In addition thereto, in the wheel supporting structure according to the Japanese Utility Model Lay-Open Print No. 55-41991, the alteration of vehicle level caused remarkable changes in the camber of the ground wheel, thus adversely affecting the wheel alignment.
As another conventional example of wheel supporting structure adapted for the adjustment of vehicle level, there was one disclosed, to be applied to an agricultural tractor, by Japanese Patent Lay-Open Print No. 59-40909, laid open Mar. 6, 1984. In this supporting structure, a wheel support casing was provided for each of front and rear ground wheels of the agricultural tractor and swingably connected, to be selectively fixed at one of a plurality of predetermined swing positions, to a stationary transmission casing which had accommodated therein a driving shaft extending in the transverse direction of the tractor. In the adjustment of vehicle level, the wheel support casing was swung relative to the transmission casing, to be fixed thereto at the desired one of the swing positions.
In this wheel supporting structure, however, the axis of the driving shaft was not coincident with that of a driving shaft disposed at the side of the wheel support casing. As a result, as the vehicle level was altered, the center of gravity of the vehicle body moved relative to corresponding one of the ground wheels in the longitudinal direction of the tractor, thus giving rise to variations in the feeling of steering operation. Additionally, this wheel supporting structure was, also, complicated and expensive.
Further, like the case of the aforesaid Japanese Patent Lay-Open Print, most agricultural tractors have rear wheels sized larger in the diameter than front wheels, so that, when equipped with such conventional wheel supporting structures, the body of such vehicle tends to rise or fall at the rear part thereof relative to the front part, with the alteration of vehicle level, thus adversely affecting the steering feeling of driver.
The present invention has been achieved to effectively solve such problems of conventional wheel supporting structures for riding type working vehicles.